| 1. |
- Grasset, Charlotte, et al.
(author)
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Can Soil Organic Carbon Fractions Be Used as Functional Indicators of Wetlands?
- 2017
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In: Wetlands (Wilmington, N.C.). - : Springer Science and Business Media LLC. - 0277-5212 .- 1943-6246. ; 37:6, s. 1195-1205
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Journal article (peer-reviewed)abstract
- This work aimed to determine whether the organic carbon in wetland soils correlated with physico-chemical characteristics of wetlands (e.g. nutrient content, pH) and differentiated wetlands according to their plant community composition definied by the CORINE Biotope nomenclature. 96 wetlands were sampled in southeastern France, belonging to 14 CORINE habitats grouped into 3 CORINE hydrological categories: wet meadows, peatlands and aquatic wetlands. The total organic carbon content, the carbon content of humic fractions (humic acid (CHA), fulvic acid (CFA) and Chumin), and water extractable organic carbon were measured in samples collected in the upper 20 cm soil layer. These soil organic carbon fractions correlated with pH and soil nutrient content but differed slightly among the 14 CORINE habitats. In contrast, soil organic carbon fractions greatly differed among the 3 CORINE hydrological categories. The CFA/CHA ratio was significantly lower for wet meadows and peatlands and the proportion of CHumin was significantly higher for peatlands and aquatic wetlands. These soil organic carbon fractions inform on the hydrological status of wetlands and may consequently be used as functional indicator in addition to a plant-based classification as the CORINE Biotope nomenclature.
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| 2. |
- Grasset, Charlotte, et al.
(author)
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Carbon allocation in aquatic plants with contrasting strategies : The role of habitat nutrient content
- 2015
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In: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 26, s. 946-955
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Journal article (peer-reviewed)abstract
- Questions: The link between the carbon composition of aquatic plants and (1) plant strategies and (2) habitat nutrient availability has received little attention. We tested whether three aquatic species belonging to the three adaptive strategies defined by Grime (ruderal, stress tolerant and competitive) had contrasting carbon allocation patterns, and if these patterns varied in the same way between populations distributed along a gradient of habitat nutrient content. Location: Wetlands in the northern Rhône River Basin, France. Methods: The three species were sampled in 17 wetlands along a gradient of nutrient content in the northern Rhône River Basin. In each population sampled, we measured plant water content, C/N ratio, structural compounds (lignin and structural polysaccharides) and storage compounds (free sugars and starch) in two seasons (spring and autumn 2012). Results: The stress-tolerant species had higher content of structural compounds than the competitive and ruderal species. The content of storage compounds was higher in the competitive and stress-tolerant species compared to the ruderal species. Allocation of carbon compounds varied with habitat nutrient content in different ways for the three species, suggesting contrasting plasticities, possibly linked to plant strategy. Conclusion: Plant strategies and habitat nutrient content are likely key drivers in plant carbon allocation and should be taken into account when studying interactions between habitat and plant quality.
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| 3. |
- Grasset, Charlotte, et al.
(author)
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Carbon emission along a eutrophication gradient in temperate riverine wetlands : effect of primary productivity and plant community composition
- 2016
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In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61, s. 1405-1420
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Journal article (peer-reviewed)abstract
- Eutrophication increases primary productivity and favours the predominance of floating vegetation in wetlands. Carbon (C) fluxes in wetlands are strongly driven by primary productivity and can differ by vegetation type. However, to the best of our knowledge, the role of eutrophication in C fluxes has rarely been assessed. Consequently, we aimed to measure the seasonal variation in carbon dioxide (CO2) and methane (CH4) fluxes at six aquatic sites in four temperate wetlands, ranging along a gradient of sediment total phosphorus content, and determine whether C fluxes correlate with above-ground net primary productivity (ANPP) and plant community composition along this eutrophication gradient. Daytime CO2 emissions were significantly and negatively correlated with wetland net primary productivity as a result of the greater C fixation by photosynthesis during the peak of production. Conversely, CH4 emissions were significantly and positively correlated with wetland ANPP, possibly due to higher litter production and anaerobic decomposition. The highest CH4 emissions were observed above floating vegetation, which favoured hypoxic conditions in the water column. CH4 emissions including ebullition were higher above macroalgal belts than above vascular plants with floating leaves. CH4 emissions without ebullition (i.e. resulting from plant transport and diffusion) better correlated with the abundance of macroalgae than with the abundance of vascular plants with floating leaves. Our results suggest that eutrophication may greatly modify CO2 and CH4 emissions from wetlands through changes in vegetation type and productivity.
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| 4. |
- Grasset, Charlotte, et al.
(author)
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Large but variable methane production in anoxic freshwater sediment upon addition of allochthonous and autochthonous organic matter
- 2018
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 63:4, s. 1488-1501
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Journal article (peer-reviewed)abstract
- An important question in the context of climate change is to understand how CH4 production is regulated in anoxic sediments of lakes and reservoirs. The type of organic carbon (OC) present in lakes is a key factor controlling CH4 production at anoxic conditions, but the studies investigating the methanogenic potential of the main OC types are fragmented. We incubated different types of allochthonous OC (alloOC; terrestrial plant leaves) and autochthonous OC (autoOC; phytoplankton and two aquatic plants species) in an anoxic sediment during 130 d. We tested if (1) the supply of fresh alloOC and autoOC to an anoxic refractory sediment would fuel CH4 production and if (2) autoOC would decompose faster than alloOC. The addition of fresh OC greatly increased CH4 production and the δ13C-CH4 partitioning indicated that CH4 originated exclusively from the fresh OC. The large CH4 production in an anoxic sediment fueled by alloOC is a new finding which indicates that all systems with anoxic conditions and high sedimentation rates have the potential to be CH4 emitters. The autoOC decomposed faster than alloOC, but the total CH4 production was not higher for all autoOC types, one aquatic plant species having values as low as the terrestrial leaves, and the other one having values as high as phytoplankton. Our study is the first to report such variability, suggesting that the extent to which C fixed by aquatic plants is emitted as greenhouse gases or buried as OC in sediment could more generally differ between aquatic vegetation types.
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| 5. |
- Grasset, Charlotte, et al.
(author)
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The transformation of macrophyte-derived organic matter to methane relates to plant water and nutrient contents
- 2019
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 64:4, s. 1737-1749
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Journal article (peer-reviewed)abstract
- Macrophyte detritus is one of the main sources of organic carbon (OC) in inland waters, and it is potentially available for methane (CH4) production in anoxic bottom waters and sediments. However, the transformation of macrophyte‐derived OC into CH4 has not been studied systematically, thus its extent and relationship with macrophyte characteristics remains uncertain. We performed decomposition experiments of macrophyte detritus from 10 different species at anoxic conditions, in presence and absence of a freshwater sediment, in order to relate the extent and rate of CH4 production to the detritus water content, C/N and C/P ratios. A significant fraction of the macrophyte OC was transformed to CH4 (mean = 7.9%; range = 0–15.0%) during the 59‐d incubation, and the mean total C loss to CO2 and CH4 was 17.3% (range = 1.3–32.7%). The transformation efficiency of macrophyte OC to CH4 was significantly and positively related to the macrophyte water content, and negatively to its C/N and C/P ratios. The presence of sediment increased the transformation efficiency to CH4 from an average of 4.0% (without sediment) to 11.8%, possibly due to physicochemical conditions favorable for CH4 production (low redox potential, buffered pH) or because sediment particles facilitate biofilm formation. The relationship between macrophyte characteristics and CH4 production can be used by future studies to model CH4 emission in systems colonized by macrophytes. Furthermore, this study highlights that the extent to which macrophyte detritus is mixed with sediment also affects CH4 production.
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| 6. |
- Isidorova, Anastasija, et al.
(author)
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Methane formation in tropical reservoirs predicted from sediment age and nitrogen
- 2019
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Journal article (peer-reviewed)abstract
- Freshwater reservoirs, in particular tropical ones, are an important source of methane (CH4) to the atmosphere, but current estimates are uncertain. The CH4 emitted from reservoirs is microbially produced in their sediments, but at present, the rate of CH4 formation in reservoir sediments cannot be predicted from sediment characteristics, limiting our understanding of reservoir CH4 emission. Here we show through a long-term incubation experiment that the CH4 formation rate in sediments of widely different tropical reservoirs can be predicted from sediment age and total nitrogen concentration. CH4 formation occurs predominantly in sediment layers younger than 6-12 years and beyond these layers sediment organic carbon may be considered effectively buried. Hence mitigating reservoir CH4 emission via improving nutrient management and thus reducing organic matter supply to sediments is within reach. Our model of sediment CH4 formation represents a first step towards constraining reservoir CH4 emission from sediment characteristics.
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